1. Field of the Invention
This invention relates to a method and apparatus which is so constructed as to utilize the heat of an exhaust gas discharged from a site of combustion for the purpose of heating such an oxidizing agent as air which is intended for the combustion.
2. Description of the Prior Art
In the combustion apparatuses which are used in such industrial furnaces as forging furnaces, normalizing furnaces, and pipestill heaters and boilers, the heat recovery type combustion apparatuses which are so configured as to utilize the heat of an exhaust gas discharged from a site of combustion for the purpose of heating such an oxidizing agent as air which is intended for the combustion have been finding general acceptance.
The words "oxidizing agent" as used herein constitute themselves the generic term for designating such gases as pure oxygen, air and oxygen-enriched air which contain oxygen gas or oxygen molecules. In some case, such oxidizing elements as halogen and such oxidizing compound as nitrogen oxide may be used as the oxidizing agent.
The recuperator which is used in these combustion apparatuses is generally provided with a specific heat exchanger interposed between an exhaust gas line and a combustion air line which are closely disposed to each other and, therefore, is enabled to exchange heat between the oxidizing agent and the exhaust gas flowing through the two lines and utilize the heat of the exhaust gas resulting from combustion for heating the oxidizing agent to be used for the combustion. The heat which is recovered by means of this recuperator is about 50% in point of temperature level. In the case of an industrial furnace which gives rise to exhaust gas of a temperature of 1,200.degree. C., for example, the oxidizing agent which has exchanged heat with the exhaust gas has a temperature of about 600.degree. C.
The recuperator is heavily restricted in point of not only material for the construction thereof but also space for the installation thereof. It possibly occupies more floor space than the main body of a furnace or a heating apparatus.
Recently, the present inventor has proposed a combustion apparatus (Japanese Unexamined Patent Publication No. 222,102/1989) which is configured as illustrated in FIGS. 9 and 10.
This heat recovery apparatus 100 is provided with a burner 112 for heating a substance W subjected to the heating inside the main body R of a furnace. In the wall of the furnace near the burner 112 is disposed a regenerative member 122 made of an air-pervious ceramic material, with a cylindrical shape and to be partitioned to the pattern of a honeycomb. This regenerative member 122 absorbs the heat of the hot exhaust gas when this exhaust gas is discharged from within the main body R and allows this heat for heating the oxidizing agent which is passing through an air path 119. The supply of the heat to the oxidizing agent is continued by causing the regenerative member 122 by a motor M through a rotary shaft 123.
However, since this heat recovery apparatus 100 must rotate the regenerative member 122 exposed to the interior of the main body R which is destined to rise to a high temperature, it is required either to interpose between the rotary shaft 123 and the motor M heat-insulating means capable of intercepting the heat transmitted from the regenerative member 122 via the rotary shaft 123 to the motor M or to set the motor M at a position so distant as to disrupt the thermal effect of the regenerative member 122. The provision of these means adds to the size of the heat recovery apparatus 100 or complicates the whole configuration thereof.
Further, the regenerative member 122 of this heat recovery apparatus 100 remains at an elevated temperature while in service and at a low temperature while out of service and alternates expansion and shrinkage in spite of the ceramic material thereof. When the regenerative member made of the ceramic material which alternates expansion and shrinkage as described above must be rotated, it is allowed a desired increase in size only with difficulty. A combustion apparatus with a-large capacity for combustion which consumes the oxidizing agent and discharges the exhaust gas both in huge volumes, therefore, is not easily attained.
Further, the regenerative apparatus which alternates expansion and shrinkage and, at the same time, rotates renders it difficult to set the burner in place at the center thereof. It, therefore, has the disadvantage in that the burner and the oxidizing agent path are separated from each other, the flexibility with which the size, sharpness, etc. of a flame emitted from the burner are controlled is degraded, and the capacity for control or versatility dwindles. Though various electrical control devices may be used for the purpose of improving the controllability of the burner, for example, the use of these devices is not desirable because they increase the cost of the apparatus as a whole.